A number of factors can affect the physical and chemical properties of compounds. One important factor is the electronegativity of atoms inside a molecule. Electronegativity is a measure of the tendency of an atom to attract bonding electrons toward itself. This property of atom affects the bond polarity and, in turn, how molecules will interact with other molecules. In this article, electronegativity and its effect on compounds will be discussed.

In the previous lecture, we talked about the affinity of nuclear positive charge for electrons. We talked about it in the context of ionic bonding and we also talked about it in the context of covalent bonding. And this relates to the Pauling scale that we alluded to earlier as well. Here is just a quick revision of that scale. If you look at the periodic table representation shown here on the board, you’ll see that the increase in electronegativity follows an increase in atomic number running from group I to Group VII and that increase in electronegativity is associated with the smallest number of shells running from the highest period to the lowest. Large atoms have a low affinity because the electrons are a long way from a positive nucleus. The core electrons shield the outer electrons from the nuclear charge. And, going across the periodic table, the affinity for bonding electrons increases because nuclear charge increases without a significant change in the distance of the electrons from the nucleus. And this is okay in explaining how we observe bond polarisation in covalent bonds and also where we see ionic bonds forming. Fluorine is the most electronegative atoms with a value of 4.0 on the Pauling scale. And remember that Group 18, or Group 8 depending on your periodic table elements, do not react: they are the noble gases and therefore their shells are already full and they are unreactive. All other elements have smaller values on the Pauling scale. And in bonds between atoms of different elements, the bonding electrons can be shared unequally. Let’s have a look for example at carbon bonded to oxygen. Note I’ve shown you a sigma bonding: a single carbon-to-oxygen bond. If we look at the individual values on the Pauling scale for...